Generally, a washing machine is an apparatus which washes clothing articles using electricity, and types of the washing machine include a drum-type washing machine in which a rotary tub is horizontally disposed and laundry items are washed by being lifted upward and lowered along an inner circumferential surface of the rotary tub when the rotary tub rotates back and forth about a horizontal axis, and a vertical-axis washing machine in which a rotary tub having a pulsator therein is vertically disposed and laundry items are washed using a water current generated by the pulsator when the rotary tub rotates back and forth with about a vertical axis.
Generally, the drum-type washing machine includes a cabinet, a tub that retains wash water inside the cabinet, and a drum that accommodates laundry items and is rotatably installed inside the tub. An opening is provided at the cabinet, and the opening is provided to be opened and closed by a door.
With laundry items, detergent, and wash water are inserted in the drum, the drum rotates to agitate the laundry items together with the wash water in order to remove dirt on the laundry items.
In this process, the laundry items are inserted through the opening provided at the cabinet, and the detergent and the wash water are provided to be fed by a detergent feed device.
However, once a washing operation of the drum-type washing machine begins, the door of the drum-type washing machine remains locked. Thus, in order to open the door during a washing process, it is required to either wait until the washing operation is finished or stop the washing operation and wait until draining of wash water is finished. Thus, there is a problem of a limitation on additionally inserting laundry items or detergent into the drum during the washing process.